A 100-kilogramme aircraft propeller which fell off a Regional Express flight will be recovered after being discovered in a southwest Sydney national park.

Police guarded the propeller overnight at the Georges River National Park in Revesby where a crime scene was established following the discovery.

The propeller, which sheared off Friday's Rex flight from Albury to Sydney, was spotted on Tuesday by a police helicopter.

It was located about 18 kilometres from the airport after the Australian Transport Safety Bureau calculated its likely trajectory using data from the aircraft's flight data recorder.

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Investigators have been assessing how best to pick up and then transport the bulky item on Wednesday.

Regional Express has grounded five aircraft following the incident. Photo / AP
Regional Express has grounded five aircraft following the incident. Photo / AP

Regional Express's bad luck continued on Tuesday afternoon when a flight bound for Griffith was forced to return to Sydney Airport with cabin pressure problems.

The airline has temporarily grounded five planes "through an abundance of caution" while it replaces gear boxes and shafts from the same series as the propeller which detached on Friday.

Two are freight services while the other three Saab 340s operate on the Melbourne and Sydney networks.

The maintenance is expected to cause only minor delays over the next two days, a spokeswoman told AAP.

AAP RY/EVT

-AAP